Advice on fixing unwanted master inheritance:

Advice on fixing unwanted master inheritance:

[Thomas Hellstrom]

Hi, all!

There's an odd master inheritance going on in drm. Consider the
following scenario.

1) Xorg opens DRM. Becomes master.
2) Plymouthd opens a file descriptor to drm.
3) Xorg exits.
4) Plymouthd calls drmSetMaster(). At this point it actually inherits
Xorg's master structure and all authenticated clients.
5) vmwgfx dislikes this and throws a BUG().

I can of course fix vmwgfx up to not throw a bug in this case, but I
figure this behavior is not really what we want, so I'd like to fix the
root cause as well, As I see it, we have two options.

A) If the client is authenticated with the master we allow the above
behaviour as a way to change master role in a master realm. If the
client is not authenticated, like Plymouthd in this case, we create a
new master structure for Plymouthd.

B) This behaviour is not allowed at all. We always create a new master
structure when this happens.

Opinions?

Thanks,
Thomas
 

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Re: Advice on fixing unwanted master inheritance:

[Dave Airlie]

On 30 November 2015 at 03:44, Thomas Hellstrom <thellstrom@vmware.com> wrote:
> Hi, all!
>
> There's an odd master inheritance going on in drm. Consider the
> following scenario.
>
> 1) Xorg opens DRM. Becomes master.
> 2) Plymouthd opens a file descriptor to drm.
> 3) Xorg exits.
> 4) Plymouthd calls drmSetMaster(). At this point it actually inherits
> Xorg's master structure and all authenticated clients.
> 5) vmwgfx dislikes this and throws a BUG().
>
> I can of course fix vmwgfx up to not throw a bug in this case, but I
> figure this behavior is not really what we want, so I'd like to fix the
> root cause as well, As I see it, we have two options.
>
> A) If the client is authenticated with the master we allow the above
> behaviour as a way to change master role in a master realm. If the
> client is not authenticated, like Plymouthd in this case, we create a
> new master structure for Plymouthd.
>
> B) This behaviour is not allowed at all. We always create a new master
> structure when this happens.
>
> Opinions?

Do we have a use case where we hand over master between server/client
I can't think of one, I'd try B first and see if anything breaks.

Dave.
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